Method of imploding frangible capsules used in well treatments



Sept. 20, 1966 J. KARPOVICH METHOD OF IMPLODING FRANGIBLE CAPSULES USED IN WELL TREATMENTS Filed Jan. 20, 1964 4 Tram [n9 Ip/UKO/ wf/h prop 0mg age/72.

Trea I I/79 [ya/ 0 INVENTOR. John K0 00 VIC 1 Gas reserve/r draw works United States Patent ()fiFice 3,273,642 Patented Sept. 20, 1966 Delaware Filed Jan. 20, 1964, Ser. No. 340,852 4 Claims. (Cl. 166-39) This is a cOntinuati-on-in-part of my application Serial Number 52,884, filed August 30, 1960, now abandoned, for Method of Imploding Frangi'ble Capsules.

This invention relates to the imploding of frangible capsules and particularly to a method of imploding frangible capsules which are disposed in a substantially liquid medium under pressure.

It is known to treat earth wells by lowering into bore holes one or more implodable frangible hermetically sealed vessels or capsules such as sealed glass vessels which are usually either evacuated or contain gases at relatively low pressures as compared to atmospheric pressure or .to the pressure of their surrounding medium in a well bore. Such capsules are usually surrounded by a liquid medium which then is placed under pressure which is sufficient to cause implosion of the capsule. The resulting violent action is of benefit in initiating formation fractures, cleaning the surface of the bore hole wall, cleaning the pores of the adjacent formation, and other well stimulation techniques.

Sometimes it is impractical to implode a capsule because the formation accepts the liquid being pumped into the well at a rate which prevents the buildup of the required implosion pressure.

Accordingly, it is a principal object of this invention to provide an improved method of imploding a hollow frangible vessel or capsule.

In accordance with this invention there is provided a frangible, sealed vessel or capsule having an electrically energizable filament therein, the capsule also containing finely divided oxidizable metal plus gaseous oxygen. The vessel, when disposed in a liquid medium under pressure, is imploded by energizing the filament to ignite the readily oxidizable metal, the ignition inducing thermal shock in the capsule wall, causing the collapse of the walls either by the shock itself or by the shock combined with the hydraulic pressure existing in the well bore at the time the filament is energized.

The invention, as well as additional objects and advantages thereof, will best be understood when the following detailed description is read in connection with the accompanying drawing, in which:

FIG. 1 is a diagrammatical View, partly in section, of a frangible capsule in accordance with this invention shown disposed in an earth well, and

FIG. 2 is a side elevational view, partly in section, of another embodiment of a frangible capsule made in accordance with this invention.

Referring to FIG. 1, there is shown an earth well 8 having a bore wall 10 which extends from the surface 12 of the earth through earth formations 14, 16, 18, for example. Casing 20, capped by a suitable casing head 22, extends through the earth formations 14, 16 and into the formation 18 near the bottom 24 of the well. The casing 20 is bonded to the wall 10 by cement 26.

A frangible capsule, indicated generally by the numeral 28, is shown suspended from a cable 30 below the casing 20 in the well 8. The cable 30 passes through the casing head 22, over a sheave 32 and to a draw works (not shown).

Usually the capsule 28 is surrounded by a strap-like harness (not shown) having a weighted lower end part, as is well known in the art. The weighted harness assures that the capsule and harness will sink towards the bottom of the bore hole while suspended from the cable.

The capsule 28 comprises a frangible body part 34 which is a hollow fiuidtight vessel having a pair of electrical leads 36, 38 extending therethrough near its upper end. A filament 40 which is capable of being heated to incandescence is connected across the leads 36, 38 inside the capsule body 34. Finely divided readily oxidizable metal 42 is disposed within the capsule, some of it being in contact with the filament 40. Oxygen is also sealed into the capsule, in an amount which is equal'to or slightly less than the amount required to react with the oxidizable metal 42. In any event, the pressure existing in the capsule after the oxidizable metal is ignited is substantially less than enough to burst the capsule because of the combination of the oxygen with the metal.

The leads 36, 38 in the capsule are electrically connected to conductors in the cable 30 and are shown schematically as being coupled at the surface to a battery 68 or other suitable electrical energizing source, through leads 70, 72 and switch 74.

A source 44 of treating fluid, a source 46 of treating fluid with propping agent, and a gas reservoir 48 are coupled to the well through the lines 51, 53, 54, valves 56, 58, 60, 62 and pumps 64, 66.

A vent valve 76 and pressure guage 78 are coupled to the casing head 22.

In operation, with the casing head 22 opened, the capsule 28 is lowered into the well 8 on the cable 30' and weighted harness (not shown) to the required depth adjacent the earth formation to be stimulated. For the sake of simplicity, the electrical coupling between the cable 30 and capsule 28 has been shown only schematic ally.

The well bore may be, if desired, at least partially filled with liquid as the capsule 28 is lowered into position.

When the capsule is in position, as at 50, near the bottom of the bore hole, the casing head is closed and, with valves 60, 62 closed, treating fluid from the reservoir 44 is pumped by means of pump 66 into the well 8. The vent valve 76 is opened until the Well bore is filled with treating fluid 52 and is then closed while the pumping of treating fluid is continued. In some cases sufficient hydrostatic pressure on the capsule for the purpose of this invention may be reached by only partially filling the well.

After the vent valve is closed, it is sometimes desirable to open valve 62 and, by means of pump 64, inject gas from the reservoir 48 into the well bore along with the liquid being pumped into the well, since (a) the column may be pressurized in this way and (b) a mix ture of gas and liquid may be recovered from the treated formation after the treatment is completed.

When the pressure on the capsule 28 is at the desired level at least half the pressure required to fracture said formation, the switch 74 is closed, energizing the filament 40 through the cable 30, and causing the ignition of the finely divided readily oxidizable metal 42 in the oxygen rich atmosphere of the capsule, to substantially instantaneously raise the temperature in said vessel to a temperature much above the temperature of the medium surrounding the vessel. The thermal stresses occurring as a result of the burning of the metal 42 produces strains in the walls of the capsule 28 which, under the pressure existing in the well bore, result in implosion of the capsu e.

Following the implosion which causes fracturing of the adjacent earth formation, the injection of treating fluid, liquid or liquid and gas, with propping agent is begun with valve 56 closed and valve 60 open, and the well treatment completed as is well known in the well fracturing art.

The finely divided readily oxidizable metal may be in the form of powder, wool or thin ribbons of magnesium, aluminum, or zirconium, for example. The gaseous reactants, usually oxygen and nitrogen, contained in the capsule are preferably present in an amount which will combine with the oxidizable metal to form solids, leaving the vessel or capsule at least somewhat evacuated at the time of its implosion. If finely divided particles of readily oxidizable metal are used, they may be painted on the wall of the capsule.

While the embodiment of the capsule shown in FIG. 1 shows the leads 36, 38 passing through the wall of the capsule, other means for accomplishing the same result are shown in FIG. 2.

In FIG. 2 the capsule 80 has an open end 82 which is adapted to receive a stopper 84 through which extend electrical leads 86, 88. When the desired atmosphere is present in the capsule with the finely divided metal 90 in place, the stopper with the electrical leads and filament 92 is placed in the open end 82, sealing the capsules. The filament preferably makes physical contact with some of the metal 90.

Thus, the present invention provides means for imploding a frangible hollow vessel or capsule which is independent of any specific hydraulic pressure being achieved in the well bore.

It is also anticipated that the battery 68 may be included in a sealed pack adjacent to the vessel 28 and that mechanical or pressure actuated switch means will be provided to close the filament energizing circuit. Such arrangement avoids the use of the relatively expensive cable 30 having insulated conductors.

What is claimed is:

1. A method of imploding in a bore hole adjacent to an earth formation a frangible sealed hollow vessel having ignitable internal heating means therein, comprising disposing said vessel in a generally liquid medium in a bore hole, pressurizing said medium to a pressure equal to at least half the pressure required to fracture said formation, and then igniting said internal heating means to substantially instantaneously raise the temperature of said vessel to a temperature much above the temperature of said medium, whereby the combination of the thermal stresses created in said walled vessel and the lower internal pressure of the vessel as compared with the higher pressure of the medium cause said vessel to implode.

2. A method in accordance with claim 1, wherein said internal heating means is finely divided readily oxidizable metal.

3. A method in accordance with claim 1, wherein said vessel is a ceramic vessel.

4. A method in accordance with claim 1, wherein said internal heating means is adhered to said vessel.

References Cited by the Examiner UNITED STATES PATENTS 2,361,558 10/1944 Mason 16643- 2,955,447 10/1960 Fink et a1. 673l 3,134,437 5/1964 Karpovich 16642.l

OTHER REFERENCES Setser, D. D.: Implosion Technique Improves Fracturing Performance, World Oil, March 1960, pp. 100- 103.

CHARLES E. OCONNELL, Primary Examiner.

D. H. BROWN, Assistant Examiner. 

1. A METHOD OF IMPLODING IN A BORE HOLE ADJACENT TO AN EARTH FORMATION A FRANGIBLE SEALED HOLLOW VESSEL HAVING IGNITABLE INTERNAL HEATING MEANS THEREIN, COMPRISING DISPOSING SAID VESSEL IN A GENERALLY LIQUID MEDIUM IN A BORE HOLE, PRESSURIZING SAID MEDIUM TO A PRESSURE EQUAL TO AT LEAST HALF THE PRESSURE REQUIRED TO FRACTURE SAID FORMATION, AND THEN IGNITING SAID INTERNAL HEATING MEANS TO SUBSTANTIALLY INSTANTANEOUSLY RAISE THE TEMPERATURE OF SAID 